The potential outcomes that you do not (and cannot) observe are known as counterfactuals because they are counter to fact (reality). “Potential outcomes” are sometimes referred to as “counterfactual outcomes,” but we will never do that in this book because a potential outcome 𝑌(𝑡) does not become counter to fact until another potential outcome 𝑌(𝑡 0 ) is observed. The potential outcome that is observed is sometimes referred to as a factual. Note that there are no counterfactuals or factuals until the outcome is observed. Before that, there are only potential outcomes